Transcutaneous capacitive data link

ABSTRACT

An implantable medical device includes a transcutaneous capacitive data link circuit. The link circuit include: a first pair of capacitors each having an external electrode configured to be externally positioned on a recipient and an internal electrode configured to be internally positioned in the recipient; a first voltage driver having positive and negative terminals each connected to one of the external electrodes, and configured to generate a first voltage drive signal responsive to a first input control signal; and a first differential amplifier circuit connected to the internal electrodes, configured to generate a first output data signal representative of the first input control signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/482,880, entitled “Transcutaneous Capacitive Data Link,” filed onJul. 10, 2006, now U.S. Pat. No. 8,315,705, which is acontinuation-in-part of International Application No. PCT/AU2005/001658,entitled “Transcutaneous Capacitive Data Link,” filed Oct. 28, 2005, nowexpired, which claims the priority of U.S. Provisional Application No.60/622,602, entitled “Coupling Out Telemetry Data in a TranscutaneousTransfer System,” filed Oct. 28, 2004, and U.S. Provisional ApplicationNo. 60/622,612, entitled “Transcutaneous Capacitive Data Link,” filedOct. 28, 2004. The entire disclosure and contents of the aboveapplications are hereby incorporated by reference herein.

This application is related to U.S. patent application Ser. No.10/883,809, now U.S. Pat. No. 7,171,273, Ser. No. 10/856,823, now U.S.Pat. No. 8,412,341, Ser. No. 10/333,676, now U.S. Pat. No. 7,502,653,Ser. No. 10/887,894, now U.S. Pat. No. 7,860,572 and Ser. No.10/887,893, now U.S. Pat. No. 8,223,982 and U.S. Pat. Nos. 6,810,289,6,751,505, and 6,700,982 which are hereby incorporated by referenceherein.

BACKGROUND

1. Field of the Invention

The present invention relates generally to transcutaneous transfersystems and, more particularly, to a transcutaneous capacitive datalink.

2. Related Art

The use of implantable medical devices to provide therapy to individualsfor various medical conditions has become more widespread as theadvantages and benefits such devices provide become more widelyappreciated and accepted throughout the population. In particular,devices such as hearing aids, implantable pacemakers, defibrillators,functional electrical stimulation devices such as cochlear prostheses,organ assist or replacement devices, and other medical devices, havebeen successful in performing life saving and/or lifestyle enhancementfunctions for a number of individuals.

Medical devices often include one or more sensors, processors,controllers or other functional electrical components that arepermanently or temporarily implanted in a patient. Many such implantabledevices require power and/or require communications with externalsystems that are part of or operate in conjunction with the medicaldevice. One common approach to provide for the transcutaneous transferof power and/or communications with an implantable component is via atranscutaneous transfer system.

One type of medical device that may include a transcutaneous transfersystem is a Cochlear™ prosthesis (commonly referred to as Cochlear™prosthetic devices, Cochlear™ implants, Cochlear™ devices, and the like;simply cochlear implant herein.) Cochlear implants provide the benefitof hearing to individuals suffering from severe to profound hearingloss. Hearing loss in such individuals is due to the absence ordestruction of the hair cells in the cochlea which transduce acousticsignals into nerve impulses. Cochlear implants essentially simulate thecochlear hair cells by directly delivering electrical stimulation to theauditory nerve fibers. This causes the brain to perceive a hearingsensation resembling the natural hearing sensation normally delivered tothe auditory nerve.

Conventional cochlear implants primarily include external componentsdirectly or indirectly attached to the body of the patient (sometimesreferred to herein as the recipient), and internal components which areimplanted in the patient. The external components typically comprise amicrophone for detecting sounds, a speech processor that converts thedetected sounds into a coded signal, a power source, and an externaltransmitter antenna coil. The internal components typically comprise aninternal receiver antenna coil, a stimulator located within a recess ofthe temporal bone of the recipient, and an electrode array positioned inthe recipient's cochlear.

Collectively, the external transmitter antenna coil and the internalreceiver antenna coil form an inductively-coupled transcutaneoustransfer system. The external transmitter antenna coil is usuallypositioned on the side of a recipient's head directly facing theimplanted antenna coil to allow for the coupling of the coils totransfer energy and data between the external and internal antennacoils. Typically, the transfer of energy is controlled to effect thetransmission of the coded sound signal and power from the externalspeech processor to the implanted stimulator unit, and to effect thetransmission of telemetry data from the implanted stimulator unit to theexternal speech processor.

SUMMARY

According to one aspect of the present invention, there is provided animplantable medical device, comprising a transcutaneous capacitive datalink circuit. The transcutaneous capacitive data link circuit comprises:a first pair of capacitors each having an external electrode configuredto be externally positioned on a recipient and an internal electrodeconfigured to be internally positioned in the recipient; a first voltagedriver having positive and negative terminals each connected to one ofthe external electrodes, and configured to generate a first voltagedrive signal responsive to a first input control signal; and a firstdifferential amplifier circuit connected to the internal electrodes,configured to generate a first output data signal representative of thefirst input control signal.

According to another aspect of the present invention, there is aprovided an a transcutaneous capacitive data link circuit. Thetranscutaneous capacitive data link circuit comprises: a first pair ofcapacitors each having an external electrode configured to be externallypositioned on a recipient and an internal electrode configured to beinternally positioned in the recipient; first voltage driver means,having positive and negative terminals each connected to one of theexternal electrodes, for generating a first voltage drive signalresponsive to a first input control signal; and first differentialamplifier means connected to the internal electrodes, for generating afirst output data signal representative of the first input controlsignal.

According to a yet another aspect of the present invention, there isprovided a a transcutaneous capacitive data link circuit is disclosed,the circuit comprising: a first pair of capacitors each having anexternal electrode configured to be externally positioned on a recipientand an internal electrode configured to be internally positioned in therecipient; a first voltage driver having positive and negative terminalseach connected to one of the external electrodes, and configured togenerate a first voltage drive signal responsive to a first inputcontrol signal; and a first differential amplifier circuit connected tothe internal electrodes, configured to generate a first output datasignal representative of the first input control signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described herein in conjunctionwith the accompanying drawings, in which:

FIG. 1A is a perspective view of internal and external components of acochlear implant system shown in their operational position on arecipient;

FIG. 2A is a perspective view of an external transmitter unit and aninternal receiver unit with external and internal electrodes shownjuxtaposed to each other, in accordance with one embodiment of thepresent invention; and

FIG. 2B is a simplified schematic diagram a capacitive data link inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention are directed to the transcutaneoustransfer of data using a capacitive link thereby providing for thelow-power transmission of data across the skin of a patient without agalvanic connection.

Embodiments of the present invention are described below in connectionwith one embodiment of an implantable medical device, namely a type ofauditory prosthesis commonly referred to as a cochlear implant. As usedherein, the term “cochlear implant” refers to any partially- orcompletely-implantable device that provides electrical stimulationand/or mechanical stimulation to a patient to improve and/or providehearing sensations. It should be appreciated, however, that the presentinvention may be implemented in connection with other types of medicalimplants as well.

Cochlear implants use direct electrical stimulation of auditory nervecells to bypass absent or defective hair cells that normally transduceracoustic vibrations into neural activity. Such devices generally usemulti-contact electrodes inserted into the scala tympani of the cochleaso that the electrodes may differentially activate auditory neurons thatnormally encode differential pitches of sound. Such devices are alsoused to treat a smaller number of patients with bilateral degenerationof the auditory nerve. For such patients, a cochlear prosthetic deviceprovides stimulation of the cochlear nucleus in the brainstem.

Exemplary cochlear implants in which embodiments of the presentinvention may be implemented include, but are not limited to, thosesystems described in U.S. Pat. Nos. 4,532,930, 6,537,200, 6,565,503,6,575,894 and 6,697,674, which are hereby incorporated by referenceherein. A representative example of a cochlear implant is illustrated inFIG. 1. FIG. 1 is a cut-away view of the relevant components of outerear 101, middle ear 102 and inner ear 103, along with a perspective viewof the components of a cochlear implant 100.

In a fully functional ear, outer ear 101 comprises an auricle 105 and anear canal 106. An acoustic pressure or sound wave 107 is collected byauricle 105 and channeled into and through ear canal 106. Disposedacross the distal end of ear cannel 106 is a tympanic membrane 109 whichvibrates in response to acoustic wave 107. This vibration is coupled tooval window or fenestra ovalis 110 through three bones of middle ear102, collectively referred to as the ossicles 111 and comprising themalleus 112, the incus 113 and the stapes 114. Bones 112, 113 and 114 ofmiddle ear 102 serve to filter and amplify acoustic wave 107, causingoval window 110 to articulate, or vibrate. Such vibration sets up wavesof fluid motion within cochlea 116. Such fluid motion, in turn,activates tiny hair cells (not shown) that line the inside of cochlea116. Activation of the hair cells causes appropriate nerve impulses tobe transferred through the spiral ganglion cells (not shown) andauditory nerve 150 to the brain (not shown), where they are perceived assound. In deaf persons, there is an absence or destruction of the haircells. Cochlear implant 100 is needed to directly stimulate the ganglioncells to provide a hearing sensation to the recipient.

FIG. 1 also shows how a cochlear implant 100 is positioned in relationto outer ear 101, middle ear 102 and inner ear 103. Cochlear implant 100comprises external component assembly 123 which is directly orindirectly attached to the body of the recipient, and an internalcomponent assembly 124 which is temporarily or permanently implanted inthe recipient.

External component assembly 123 comprises microphone 125 for detectingsound which is outputted to a BTE (Behind-The-Ear) speech processingunit 126 that generates coded signals and are provided to an externaltransmitter unit 128, along with power from a power source such as abattery (not shown). External transmitter unit 128 comprises an externalcoil 130 and, preferably, a magnet (not shown) secured directly orindirectly to the external coil.

Internal component assembly 124 comprises an internal receiver unit 132having an internal coil (not shown) that receives power and codedsignals from external assembly 123. Internal receiver unit 132 transmitsthe received power and coded signals to a stimulator unit 120 whichapplies the coded signal to an electrode assembly 144 disposed on thedistal end of a carrier member 140. Electrode carrier member 140 enterscochlea 116 at cochleostomy 122 such that one or more electrodes 142 ofelectrode assembly 144 are aligned with portions of cochlea 116.

Cochlea 116 is tonotopically mapped with each region of the cochleabeing responsive to acoustic and/or stimulus signals in a particularfrequency range. To accommodate this property of cochlea 116, electrodes142 are each constructed and arranged to deliver appropriate stimulatingsignals to particular regions of cochlea 116, each representing adifferent frequency component of a received audio signal. Signalsgenerated by stimulator unit 120 are applied by the electrodes 142 ofelectrode array 144 to cochlea 116, thereby stimulating the auditorynerve 150. It should be appreciated that although in the embodimentshown in FIG. 1 electrodes 142 are arranged in array 144, otherarrangements are possible.

As noted, cochlear implant 100 comprises an embodiment of a capacitivedata link system of the present invention to transmit data betweeninternal components 124 and external components 123. A simplifiedschematic diagram of embodiments of such a capacitive data link systemis depicted in FIG. 2A and FIG. 2B. As shown in FIG. 2A, a capacitivedata link system 200 comprises external components 202 and internalcomponents 204. External components 204 are worn by the recipient, forexample, integrated into speech processor 126 (FIG. 1), or as aseparately-worn unit connected to speech processor 126 by a cable. Theoperational connection to speech processor 126 is generally representedby line 203. Internal components 204 are implanted in the recipient at alocation in which a capacitive link may be established, as describedherein. Internal components 204 are operatively coupled to stimulatorunit 120 (FIG. 1). The operational connection to stimulator unit 120 isgenerally represented by line 201.

In this exemplary embodiment, capacitive data link system 200 comprisestwo capacitors 206A and 206B. Each capacitor 206 comprises twoelectrodes capacitively coupled across skin 208. Specifically, externalcomponent assembly 202 comprises an external electrode 210A and 210B ofcapacitors 206A and 206B, respectively. External component assembly 202also comprises a voltage driver 212 (FIG. 2B) which generates a biphasicvoltage signal 214 to differentially drive external electrodes 210 ofcapacitors 206 as described herein. Voltage driver 212 is responsive toinput control signals 230 generated by speech processing unit 126.

Internal component assembly 204 comprises internal electrodes 216A and216B of capacitors 206A and 206B, respectively. Each internal electrodes216A, 216B is connected to one input of a differential amplifier 218(FIG. 2B) through a resistive network 220. Differential amplifier 218generates an output data signal 222 which is received by stimulator unit120 (FIG. 1). Because changes in voltage drive signal 214 are reflectedin output data signal 222, speech processing unit 126 may transmit datato stimulator unit 120 by controlling voltage driver 212.

It should be appreciated that the embodiment illustrated in FIG. 2B is asimplified schematic. For example, as one of ordinary skill in the artwould appreciated, embodiments of internal component assembly 204 wouldtypically include signal conditioning circuitry to convert output datasignal 222 generated by differential amplifier 218 to a form suitablefor use by stimulator unit 120 or other internal component 124 of system100. Such signal conditioning circuitry may include, for example, acomparator, pulse forming circuitry and related circuitry and/or othercircuitry to amplify and shape output data signal 222 as required forthe particular application.

Capacitors 206A and 206B each comprise oppositely-spaced electrodes210A/216A and 210B/216B; that is, the opposing electrodes 210, 216 ofeach capacitor 206 are aligned with each other along an axis linesubstantially orthogonal to planes defined by the electrodes. Suchtranscutaneous alignment facilitates the capacitive coupling attained byeach capacitor 206 during operation of capacitive data link system 200.In the embodiment shown in FIG. 2A, such alignment is attained by theuse of magnets 228A and 228B.

External electrodes 210 are adjacent to and preferably not in contactwith skin 208 of the recipient. Accordingly, external electrodes 210 maybe encased in a housing formed of a suitable dielectric material. Suchhousing may provide a desired separation between external electrodes 210and the recipient and, therefore, between external electrodes 210 andinternal electrodes 216.

Internal electrodes 216, on the other hand, are galavanically isolatedfrom the body of the recipient to maintain operational integrity of thedevice as well as to ensure the device is biocompatible. As such,internal capacitor electrodes 216 may be encapsulated in, for example, asilicon film.

External and internal electrodes 210, 216 may be formed of anyconductive material and may have any dimensions suitable for aparticular application. For example, in one embodiment, electrodes 210,216 comprise a conductive material such as copper or platinum metal andare formed as a flexible coil or film. Thus, it should be appreciatedthat capacitors 206 can be implemented with any conductive materialhaving any dimensions suitable for achieving a capacitive link given theparticular patient and where on the patient the capacitor is located. Itshould also be appreciated that the materials used to form the externalelectrode of a capacitor 206 need not be the same as the materials usedto form the internal electrode of that same capacitor 206.

Preferably, external electrode 210 and internal electrode 216 of eachelectrode 206 have the substantially the same dimensions and surfacearea. In addition, in many embodiments, capacitors 206 are as large aspossible to facilitate signal coupling, while taking into considerationthe limits imposed on capacitor size due to the size of the recipient'shead, the distance between opposing electrodes 210, 216 of eachcapacitor 206, etc. In one embodiment, electrodes 210, 216 arerectangular and have a surface area of approximately 1 cm³. It should beappreciated, then, that the surface area and dimensions of electrodes210, 216 may vary depending on the requirements of the particularapplication.

As one of ordinary skill in the art would appreciate, the capacitance ofeach capacitor 206 is determined by a number of factors such as thedimensions and spacing of its electrodes 210, 216, and the material,here, skin and perhaps hair, between the electrodes of the capacitor. Insome embodiments in which capacitors 206 are designed for use inconnection with a cochlear implant system such as system 100 introducedabove, the capacitance of each capacitor 206 is in the range ofapproximately 0.1 pf-0.5 pf. In alternative embodiments implemented inconnection with the same or different application, the capacitance ofeach capacitor 206 may be different, and based on a variety of factorsincluding the distance and material between electrodes 210, 216.

As noted, external components 202 include a voltage driver 212. Voltagedriver 212 generates differential voltage signal 214 to generate anelectric field change on internal electrodes 216 of capacitors 206.Preferably voltage driver 212 generates a pulse waveform, although anybiphasic waveform such as a sinusoidal waveform may be used todifferentially drive capacitors 206. In one embodiment, voltage driver212 generates a 5 volt signal for the implemented TTL circuitry. Itshould be appreciated, however, that any suitable voltage signalgenerated by any voltage source now or later developed can be used inalternative embodiments. For example, in one alternative embodiment,voltage driver 212 generates a 3 volt signal.

In one embodiment, capacitive data link system 200 is powered, forexample, by a battery. In such embodiments, the amplitude of voltagesignal 214 may be limited. In alternative embodiments, a voltage signal214 with relatively greater amplitude may be provided to support greatersignal strength. As one of ordinary skill in the art would appreciate,such a voltage boost will likely consume additional power and, thereforerequire some trade-offs.

As noted, internal electrodes 216 of capacitors 206 are connected torespective inputs of a discrete differential amplifier 218 through aresistive network 220. Differential amplifier 218 amplifies thedifference in electric potential between the two inputs. In this way,common mode variations caused not by external sources are substantiallyisolated. Preferably, differential amplifier 218 is a transistordifferential amplifier implementing JFETs due to its high inputresistance and low input capacitance. As one of ordinary skill in theart would appreciate, differential amplifier 218 may be implemented in avariety of ways with a variety of components well known in the art.

Resistive network 220 is provided to adjust the input impedance ofdifferential amplifier 218. In one embodiment, resistors 224A and 224Bare approximately 1 MOhm. It should be appreciated that the values ofresistors 224 may be selected based on conventional designconsiderations well-known to those of ordinary skill in the art. In theabove exemplary embodiment, the resulting differential voltage acrossthe inputs of amplifier 218 is approximately 20 mV. Collectively,differential amplifier 218 and resistive network 220 are referred toherein as differential amplifier circuit 226.

As understood by those of ordinary skill in the art, the current throughcapacitors 206 is determined by the rise time and the height of voltagesignal 214 generated by voltage driver 212. This also determines theamplitude of output data signal 222. The current through capacitors 206is also proportional to the size of electrodes 206. As such, the voltageprovided to the inputs of differential amplifier 218 is approximatelyproportional to its input impedance and this current.

It should also be appreciated that just a few embodiments of the presentinvention have been described herein. For example, although capacitivedata link system 200 is herein described as having components that areinternal or external to the patient, it should be understood that inanother embodiment of the present invention, the capacitive data linksystem may be configured to also have components 202 internal to thepatient, and having components 204 external to the patient, to permitbi-directional communication. A bi-directional half duplex data link maybe achieved, for example, with the addition of a multiplexer andadditional driver and receiver components. One advantage of suchembodiments is that bi-directional communication of data can be achievedwith low power usage. It should be appreciated that such bi-directionalcommunication can be half-duplex or full-duplex.

The present invention advantageously allows for the functionalseparation of data and power transmission, enabling each to be optimallyconfigured without concern for the potential adverse effects on theother type of transmission. In one embodiment of the present invention,the data rate is approximately 1 megabit per second, or 1 megahertz. Itshould be appreciated, however, that the data rate can be significantlyhigher or lower should a different data bandwidth be required.

One advantage of certain embodiments of the present invention is thathigh data transmission rates can be achieved with low power usage. Inone embodiment for example, the transmission rate is 1 MHz. It should beappreciated, however, that the transmission rate is determined by anumber of factors including, but not limited to, the skin and the hairthat are located between the external and internal plates of eachcapacitor 206.

Yet another advantage of certain embodiments of the present invention isthat longer data streams can be achieved with low power usage, than ispossible where energy and data transfers are transmitted through acombined means.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

What is claimed is:
 1. An implantable medical device, comprising: atranscutaneous capacitive data link circuit comprising: a first pair ofcapacitors each having an external electrode configured to be externallypositioned on a recipient and an internal electrode configured to beinternally positioned in the recipient; a first voltage driver havingpositive and negative terminals each connected to one of the externalelectrodes, and configured to generate a first voltage drive signalresponsive to a first input control signal; and a first differentialamplifier circuit connected to the internal electrodes, configured togenerate a first output data signal representative of the first inputcontrol signal.
 2. The implantable medical device of claim 1, whereinthe data link circuit further comprises: a second pair of capacitorseach having an external electrode configured to be externally positionedon a recipient and an internal electrode configured to be internallypositioned in the recipient; a second voltage driver having positive andnegative terminals each connected to one of the internal electrodes ofthe second pair of capacitors, and configured to generate a secondvoltage drive signal responsive to a second input control signal; and asecond differential amplifier circuit connected to the externalelectrodes of the second pair of capacitors, configured to generate asecond output data signal representative of the second input controlsignal.
 3. The implantable medical device of claim 2, wherein: thesecond input control signal comprises telemetry signals generated by animplanted stimulator unit of the implantable medical device; and thesecond output data signal is suitable for receipt by a speech processorunit of the implantable medical device.
 4. The circuit of claim 2,wherein the second differential amplifier circuit comprises: adifferential amplifier; and a resistive network connected between thedifferential amplifier and the internal electrodes.
 5. The implantablemedical device of claim 1, wherein: the first input control signalcomprises a coded sound signal generated by a speech processor unit ofan implantable medical device, and the first output control signal issuitable for receipt by an implanted stimulator unit of the implantablemedical device.
 6. The implantable medical device of claim 1, whereinthe first differential amplifier circuit comprises: a differentialamplifier; and a resistive network connected between the differentialamplifier and the internal electrodes.
 7. The implantable medical deviceof claim 1, wherein: each capacitor of the first pair thereof includesopposing electrodes; each electrode is substantially planar and has anaxis substantially orthogonal thereto; and for each capacitor, the axesof opposing electrodes thereof are substantially aligned with eachother.
 8. The implantable medical device of claim 1, wherein: theimplantable medical device is an implantable auditory prosthesis.
 9. Theimplantable medical device of claim 8, wherein: the implantable auditoryprosthesis is a cochlear implant.
 10. An implantable medical device,comprising: a transcutaneous capacitive data link circuit comprising: afirst pair of capacitors each having an external electrode configured tobe externally positioned on a recipient and an internal electrodeconfigured to be internally positioned in the recipient; first voltagedriver means, having positive and negative terminals each connected toone of the external electrodes, for generating a first voltage drivesignal responsive to a first input control signal; and firstdifferential amplifier means connected to the internal electrodes, forgenerating a first output data signal representative of the first inputcontrol signal.
 11. The implantable medical device of claim 10, whereinthe data link circuit further comprises: a second pair of capacitorseach having an external electrode configured to be externally positionedon a recipient and an internal electrode configured to be internallypositioned in the recipient; second voltage driver means having positiveand negative terminals each connected to one of the internal electrodesof the second pair of capacitors, for generating a second voltage drivesignal responsive to a second input control signal; and seconddifferential amplifier means connected to the external electrodes of thesecond pair of capacitors, for generating a second output data signalrepresentative of the second input control signal.
 12. The implantablemedical device of claim 11, wherein: the second input control signalcomprises telemetry signals generated by an implanted stimulator unit ofan implantable medical device, and the second output data signal issuitable for receipt by a speech processor unit of the implantablemedical device.
 13. The implantable medical device of claim 10, wherein:the first input control signal comprises a coded sound signal generatedby a speech processor unit of an implantable medical device, and thefirst output control signal is suitable for receipt by an implantedstimulator unit of the implantable medical device.
 14. A transcutaneouscapacitive data link circuit comprising: a first pair of capacitors eachhaving an external electrode configured to be externally positioned on arecipient and an internal electrode configured to be internallypositioned in the recipient; a first voltage driver having positive andnegative terminals each connected to one of the external electrodes, andconfigured to generate a first voltage drive signal responsive to afirst input control signal; and a first differential amplifier circuitconnected to the internal electrodes, configured to generate a firstoutput data signal representative of the first input control signal. 15.The circuit of claim 14, further comprising: a second pair of capacitorseach having an external electrode configured to be externally positionedon a recipient and an internal electrode configured to be internallypositioned in the recipient; a second voltage driver having positive andnegative terminals each connected to one of the internal electrodes ofthe second pair of capacitors, and configured to generate a secondvoltage drive signal responsive to a second input control signal; and asecond differential amplifier circuit connected to the externalelectrodes of the second pair of capacitors, configured to generate asecond output data signal representative of the second input controlsignal.
 16. The circuit of claim 15, wherein: the second input controlsignal comprises telemetry signals generated by an implanted stimulatorunit of a cochlear implant; and the second output data signal issuitable for receipt by a speech processor unit of the cochlear implant.17. The circuit of claim 15, wherein the second differential amplifiercircuit comprises: a differential amplifier; and a resistive networkconnected between the differential amplifier and the internalelectrodes.
 18. The circuit of claim 14, wherein: the first inputcontrol signal comprises a coded sound signal generated by a speechprocessor unit of a cochlear implant; and the first output controlsignal is suitable for receipt by an implanted stimulator unit of thecochlear implant.
 19. The circuit of claim 14, wherein the firstdifferential amplifier circuit comprises: a differential amplifier; anda resistive network connected between the differential amplifier and theinternal electrodes.
 20. The circuit of claim 14, wherein: eachcapacitor of the first pair thereof includes opposing electrodes; eachelectrode is substantially planar and has an axis substantiallyorthogonal thereto; and for each capacitor, the axes of opposingelectrodes thereof are substantially aligned with each other.